Process for isomerization of olefinic hydrocarbons



United States Patent Delaware No Drawing. Filed Get. 3, 1961, Ser. No.142,523

Claims. (til. 204 162) This invention relates to the isomerization ofolefins, and more particularly to isomerization etiecting a shift in thedouble bond of l-olefins having more than 3 carbon atoms in a moleculeto a more centrally located position, In its more specific aspect, thisinvention'relates to a conversion of l-butene to Z-butene. Double bondisomerization of olerinic hydrocarbons whereby the double bond isshifted from the alpha pos1 tion to a more centrally located position isknown in the art, and is useful in the production of improved motorfuels, and "as a starting material in chemical synthesis. lsomerizationconversion of the olefin is effected in the presence of a catalyst, andusually at high temperatures. Also, conversion of various hydrocarbonshas been effectively achieved in more recent years by radiolysis.

Upon exposure of the hydrocarbon fraction to irradiation, conversion ofthe hydrocarbon may result, the type of conversion reaction beingdependent upon the feed stock, conditions employed, catalyst, etc. Knownconversion reactions by reason of radiolysis include for example,hydrogenation, dehydrogenation, polymerization, alkylation, cracking,and so on. To the best of my knowledge, radiolysis of olefin-i0hydrocarbons has resulted in polymerization, irrespective of thecatalyst, if any.

This invention has therefore as its purpose to provide a process for thedouble bond isomerization of l-olefins whereby the double bond isshifted to a more centrally located position. As a further advantage,the process of this invention may be conducted at moderate temperatures.

Briefly, my invention involves a process for the double bondisomerization of l-olefins which contain more than 3 carbon atoms permolecule. In accordance with my invention, a molecular sieve adsorbentis subjected to gamma irradiation, and the olefinic hydrocarbon isadsorbcd by the activated sieve. The resultant product exhibiting thedouble bond in a more centrally located position is subsequentlydesorbed from the molecularsieve adsorbent. The shift of double bondthat occurs by reason of 'isomerization of the l-olefin molecule takesplace more often to an immediately adjacent position although some shift"of the double bond can take place over a greater portion of themolecule The olefinic feed stock for the process may be derived from anysuitable source including a pure olefin or mixture ofolefins having morethan 3 carbon atoms in the molecule. thenes may be present in the feedstock as impurities but preferably'these impurities should be inert tothe conversion reaction. However, paraffins are adsorbed by themolecular sieve adsorbent and may alfect the sieve loading with asubsequent loss in adsorption of the olefins. The feed stock, therefore,desirably containsover 50% by weight, and preferably over 775% byweight, of

l-olefins having more than 3carbon atoms per molecule. Although theinvention is .particularlyadapted to the'conversionof I-butene to2-butene,g, and is, discussed below A certain-percentage of parafiins or'naphi in detail, it should be understood that thepr oc'ess may aisssssPatented Nov. 24, 1964 be utilized for shifting of the double bond andother 1- olelins or alpha olefins to oletlns in which the double bond isin a more centrally located position, and include for example,l-pentene, l-iexene, l-heptene, l-octene, etc. Although oleiins havingas many as 20 carbon atoms per molecule may be used in the practice ofmy invention, the higher molecular weight materials become progressivelymore difilcult to adsorb, and therefore the invention is particularlysuited to olefins containing 4 to 10 atoms per molecule.

The molecular sieve adsorbent employed in my invention comprises certainalumino silicates, such as calcium alumina silicate, of inorganicmaterials in the form of porous crystals wherein the pores of thecrystal are of molecular dimension and are of uniform size. A particularsuitable adsorbent is calcium alumino silicate manufactured by Linde AirProducts Company and designated Type 131 molecular sieve, but othermolecular sieve adsorbents may be used such as Type 53 or Type 10A. Thecrystals of these calcium alumino silicate materials, apparentlyactually a sodium calcium alumina silicate, have a pore size sufficientto admit the l-olefins, the pore size or diameter for Type 131%, forexample, being about 13 Angstrom units. Molecular sieve adsorbents withthe larger pore size, especially the Type 131%, molecular sieve, isparticularly suited for absorption of larger molecules and the branchedchain molecules; and, equally important, the desorption step may beconducted more rapidly. This particular silicate adsorben is availablein various sizes such as and /s" pellets as Well as finely dividedpowder form.

In accordance with the process of the present invention the molecularsieve adsorbent is exposed to gammaray exposure dose usually at not lessthan about 5x10 roentgens, and preferably about 5 x10 to 500x10roentgcns. Where deemed desirable, a higher dosage of gamma-ray exposuremay be employed, but there appears to be no benefit in exceeding about500x10 roentgens. Any suitable source yielding gamma irradiation may beemployed such as radioactive isotopes, nuclear reactor and electronaccelerator. The dosage of gamma irradia- 'tion is dependent somewhatupon the amount of olefin to be absorbed per gram of adsorbent, a higherdosage usually being re uired with increased amount of olefin adsorbate.The lapse in time after the molecular sieve adsorbent has beenirradiated with the desired dosage and before persorbtion of thel-oleiin appears to have sub.- stantially no effect on catalystactivity. Thus, this time lapse, referred to as decay time, may extendto as much as 200 or 300 hours or more without any substantial loss incatalyst activity.

It was found that subjecting the molecular sieve absorbent to hightemperatures during or af er irradiation will cause a decrease incatalytic activity. For this reason, irradiation is conducted at arelatively moderate The l-olefin' is then adsorbed on the irradiatedmolecular sieve adsorbent. The olefinic feed stock is contacted with theadsorbent, at asuitable temperaturej'and preferably in the vapor phase.Adsorption is conducted at a temperature range between about to 100 C.,and preferably between about to 40 C. Where temperatures higher than thedescribed maximum are used, cracking, decomposition or other undesirablereactions may occur, and further will cause a decrease in catalystactivity. Although the pressure employed is not particularly critical,pressures less than one atmosphere we desirable, but it may be moreconvenient and economical to conduct the process at atmosphericconditions. However, low superatmospheric pressures may be employed, forexample, 5 atmospheres or more. Where deemed desirable, the olefinicfeed stream upon contact with the molecular sieve adsorbent may bemaintained in a liquid phase, and under high pressure. Adsorption iscontinued until the molecular sieve adsorbent has adsorbed apredetermined quantity of olefins, desirably about 0.5 to 50 cc. gaseousolefins at standard temperature and pressure (S.T.P. measured at 0 C.and 1 atmosphere of pressure) per gram of adsorbent, and more preferably1 to 30 cc. of olefin (S.T.P.) per gram of adsorbent.

The adsorbed olefin is permitted to remain in contact with the irradiatesieve for a period of time sufficient to effect substantialisomerization. time is somewhat dependent on the dosage of irradiationand the amount of olefin adsorbed per gram of adsorbent. Although thereaction time may be a few hours, e.g. 3 to 4 hours, very high yieldshave been obtained with reaction time ranging from hours to as high as200 hours.

The resultant product comprising the isomerized olefin adsorbed on themolecular sieve is desorbed or dis- This reaction the irradiatedmolecular sieve adsorbent, and the amount of hydrocarbon adsorbedthereon was determined for each sample run. The adsorption tube wascooled in liquid nitrogen to facilitate hermetic sealing of the tube,and then warmed to room temperature.

The adsorbate was desorbed from a molecular sieve adsorbent by waterdisplacement desorption. Water employed in the desorption step wasinitially degassed by alternate freezing, opening to the vacuum systemand warming. The degassed water was distilled, the vapors passed to theadsorption tube, and the desorbed hydrocarbon and excess water vaporwere collected in a tube cooled by liquid nitrogen. After the desorptionwas completed, the tube containing the desorbed product was allowed towarm up to room temperature whereby the (lesorbed product expanded andtransferred by a toepler pump through a Dry Ice trap to separate theolefinic hydrocarbon from the water. The hydrocarbon product recoveredwas measured, and a sample collected for analysis by vapor phasechromatography.

The molecular sieve adsorbent was irradiated from a cobalt 60 source,and l-butene, having a purity in excess of 99%, Was adsorbed in thesieve at room temperature. After sufiicient time for the reaction, theadsorbate was desorbed from the sieve and the product analyzed, asdescribed above. Table 1 below summarizes the conditions and results forthe numerous runs, the table showing the dosage of irradiation, theconditions for adsorption, the time for the reaction and the percentconversion. Control run A differed from the other runs only in that thecontrol was not subjected to irradiation.

T ablels0merization of Butane Conditions for Adsorption ProductDistribution (wt. percent) Irradiation, Reaction Sample N 0. RoentgensVol. Gas Time,

X10 Pressure, Temp, Adsorbcd Hrs. Ois-2- Trans-2- cm. of 0. per Grambutene buteue l-butene mercury Adsorbent,

cc. (S.'l.P.)/g.

None 0. 1 24. 4 0. 97 16 None None 100 55. 5 0. 1 24 0. 99 16 49. 5 20.3 24. 4 337 0. 1 24 1. 04 16 59. G 21. 2 l0. 2 9. 6 0. 1 24 0. 9G 16 24.2 13.5 (52. 3 8. 5 0. 1 24 10. 5 200 44. 40. 7 9. 3 9. 6 0. 1 24 40. 4l6 8. 7 2. 3 89. 9. 6 0. 1 2t 1. O8 16 1. 1 0.7 08. 2

1 Irradiated sieve material was subjected to heating at 310 C. for 4%hours before adsorption of olefinio material.

placed therefrom by known conventional means. The molecular sievematerial may be desorbed, for example, by water displacement wherebywater is passed through the sieve generally at a temperature in therange of 15 to C. The Water, having a greater afiinity for the sieve,displaces the olefinic hydrocarbon. The desorbed olefin containing somewater may be passed to any suitable recovery unit to remove the water.The molecular sieve materal may be regenerated as by heating and purgingwith an inert gasgenerally at a temperature of 150 to 250 C., and theregenerated sieve may be irradiated and contacted with fresh feed stockas explained above.

In each of the following examples, which further illustrate myinvention, adsorption tubes were packed with Linde 135 molecular sieveadsorbent material. The packed adsorbent material was degassed byinitially heating in a vacuum at a pressure of 10 mm. of mercury at 450C. for 16 hours, and the degassed material then cooled to roomtemperature. Except with control runs, each adsorption tube wassubjected to irradiation for a prescribed time from a cobalt source. Theolefinic hydrocarbon in the gaseous phase was contacted with It will beobserved from the table that it is possible to employ a relativelyshorter reaction time when using a higher gamma-ray exposure dose. Onthe other hand, when using a lower dosage of irradiation, the reactiontime may be increased as seen in run 4 which shows a high yield. Run 5shows that when the amount of olefin adsorbed on the sieve is increased,it is desirable to increase the dosage of irradiation and/or thereaction time. Run 6 illustrates the adverse effect of heating the sieveafter irradiation.

I claim:

1. A process for the double bond isomerization of l-oleiins having morethan 3 carbon atoms in the molecule comprising gamma irradiating amolecular sieve adsorbent with not less than about .5 l0 roentgens,adsorbing said l-olefin on said irradiated molecular sieve adsorbent,desorbing the molecular sieve adsorbent and recovering the resultantproduct.

2. A process according to claim 1 wherein the source for said gammairradiation is cobalt 60.

' 3. A process for the isomerization of l-butene to 2- butene comprisinggamma irradiating a molecular sieve I 5 adsorbent with not less thanabout 5x10 roentgens, adsorbing said l-butene on said irradiatedmolecular sieve, desorbing said molecular sieve and recovering Z-buteneas the resultant product.

4. A process according to claim 3 wherein about 0.5 cc. to 50 cc.gaseous butene are adsorbed on said irradiated molecular sieve adsorbentper gram of said molecular sieve adsorbent.

5. A process according to claim 3 wherein said gamma irradiation isabout 5x10 to 500x10 roentgens.

References Cited in the file of this patent UNITED STATES PATENTS2,956,941 Heath et al Oct. 18, 1960 5 FOREIGN PATENTS 842,136 GreatBritain July 20, 1960 OTHER REFERENCES Caifrey et al.: Journal ofPhysical Chemistry, volume 10 62 (January 1958), pages 33-37.

1. A PROCESS FOR THE DOUBLE BOND ISOMERIZATION OF 1-OLEFINS HAVING MORE THAN 3 CARBON ATOMS IN THE MOLECULE COMPRISING GAMMA IRRADIATING A MOLECULAR SIEVE ADSORBENT WITH NOT LESS THAN ABOUT .5X10**8 ROENTGENS, ADSORBING SAID 1-OLEFIN ON SAID IRRADIATED MOLECULAR SIEVE ADSORBENT, DESORBING THE MOLECULAR SIEVE ADSORBENT AND RECOVERING THE RESULTANT PRODUCT. 